1. Field of the Invention:
This invention relates to a toner recovery device for recovering a toner collected by a cleaning device of an electrostatic recording apparatus such as an electrophotographic copying machine into a developing unit and more specifically, to an improvement to a toner recovery device disclosed in Japanese Patent Application Laid-Open No. 30,161/1981.
2. Description of the Prior Art:
The toner recovery device disclosed in Japanese Patent Application Laid-Open No. 30,161/1981 will first be described broadly with reference to the FIGS. 1 and 2 thereof before the present invention is explained.
In the drawings, reference numeral 1 represents a photosensitive drum as a charge receptor. On the circumferential surface of this photosensitive drum 1 are disposed, sequentially and adjacent one another in the rotating direction of the drum, a charging electrode 2, an exposure optical system 3, a developing unit 4, a paper feeding device 5, a transfer electrode 6, a separation electrode 7, a transfer paper conveyor device 8, a charge eliminating electrode 9 and a cleaning device 10, in order named. The developing unit 4 accommodates a two-component system developing agent containing a magnetic carrier and an electrostatic toner and is equipped with a magnetic brush device 11 for forming ears of the electrostatic toner around the circumferential surface and with agitating blades 12 for generating the frictional charge of the electrostatic toner. A screw conveyor 13 for uniformly distributing the recovered toner is disposed at the upper part of the developing unit 4. The cleaning device 10 is equipped with a blade 15 placed in a container 14 and having its tip placed on the circumferential surface of the photosensitive drum 1. The toner scraped off from the circumferential surface of the photosensitive drum 1 by the blade 15 falls along a guide plate 16 and is collected at one of end portions of the container 14 by the screw conveyor 17 positioned at the bottom of the container 14.
The toner recovery device includes a case 18 consisting of a case main frame 18a and a cover 18b that are placed close to each other at one of end portions of the photosensitive drum 1, and a rotary member 19 made of a non-magnetic material, placed in this case 18. This rotary member 19 is driven by a sprocket 20 independently of the photosensitive drum 1 and is so constructed in a hollow as to be possessed of an outer diameter substantially equal to that of the photosensitive drum 1. Permanent magnets 21 having poles in the radial direction are equidistantly disposed on the inner circumferential surface of the rotary member 19. An endless belt 22 made of a non-magnetic material having flexibility is wound on the circumference of the rotary member 19 and is spread over an idler 23 and a tension roller 24 that are so supported by the case 18 as to face the screw conveyor 13.
In the toner recovery device having such a construction, the ears of the developing agent are formed on the surface of the endless belt 22 as the rotary member 19 is driven for rotation, and the collected toner is catched into the ears of the developing agent on the surface of the endless belt 22, thereby effecting recovery of the toner. According to the tests and examination carried out by the inventors of the present invention, however, it was found that the toner could not much be recovered as expected. Though the case main frame 18a was made of an acrylic resin with the cover 18b being made of an iron sheet, the quantity of the toner recovered into the developing unit 4 was only small and the magnetic carrier in the developing unit 4 decreased gradually. When the case 18 was disassembled, a large quantities of developing agent was found inside the case 18. According to the results of analysis made by the inventors of the present invention, it was assumed that magnetic induction was generated on the cover 18b by the permanent magnets 21 of the rotary member 19 so that the developing agent that was being carried by the endless belt 22 was attracted to the cover 18b and thus accumulated in the case 18.
It was also found that in the conventional toner recovery device, the recovery ratio gradually dropped. This was partly because the toners attaching to the endless belt 22 and the floating toners came into and between the circumferential surface of the rotary member 19 and the endless belt 22 along with the operation of the electrophotographic copying machine and these toners played the role of a lubricant and reduced the frictional force between the circumferential surface of the rotary member and the endless belt until at last the endless belt 22 no longer moved. Though the inventors of the present invention applied knurling work to the circumferential surface of the rotary member to cope with this problem, the toners entered the recesses of the knurling along with the operation of the copying machine, the result remaining substantially unaltered.